1. Field of the Invention
The invention relates to a telescopable boring rod mechanism with at least two mutually displaceable Kelly rods, which have means for transmitting a torque to the adjacent Kelly rod.
2. Related Art
Such telescopable boring rod mechanisms are required for the so-called Kelly boring method, which is one of the most flexible procedures e.g. for the production of foundation piles for buildings. The torque of the boring implement is transmitted from a turning gear, which can be moved up and down on a mast, to a boring rod mechanism, the so-called Kelly rod mechanism. The Kelly rod mechanism comprises several telescoped tubular Kelly rods, whereof the innermost rod is suspended on a cable of the implement and can therefore be moved up and down, which brings about the telescoping of the Kelly rod mechanism. The boring tool is fixed to the bottom of the innermost Kelly rod. Through more or less vertical fillets on the outside of each individual Kelly rod and corresponding vertical driving slots on the adjacent Kelly rod, in accordance with a shaft-collar connection or joint, the torque and therefore the rotary movement is transmitted from one Kelly rod to the other. Thus, the rotary movement is transmitted from the turning gear to the boring tool in the borehole.
Telescoping takes place in the following way. Initially, when the Kelly rod mechanism is completely outside the borehole, all the Kelly rods on their lower stop are located on the bottom Kelly rod, also known as the inner Kelly. The completely retracted Kelly rod mechanism is consequently suspended by means of the inner Kelly on the Kelly cable. If the Kelly rod mechanism is then lowered into the hole, at a specific time an upper stop of the Kelly rod mechanism strikes against a Kelly driver of the turning gear and rests there. During further lowering the remaining Kelly rods move downwards until the next inner Kelly rod “sticks” with its upper stop on the lower end of the outermost Kelly rod. This can be continued until the Kelly rod mechanism has been completely extended. Such Kelly rod mechanisms are e.g. known from EP 376 239 A or U.S. Pat. No. 3,517,760.
Torque can be transmitted in any extension state of the Kelly rod. The Kelly rods on the lower stop either rest on the next inner Kelly rod or they hang with their upper stop on the next outer rod. With all the Kelly rods the torque is transmitted at the upper or lower end. Only in the case of a single Kelly rod, the outermost of those resting on the innermost rod, does the Kelly driver of the next outer rod engage between the upper and lower end in the Kelly fillets and transmits torque there.
Besides the transmission of the rotary movement in the case of so-called lockable Kelly rod mechanisms, a vertical force is transmitted from the slide on which the turning gear moves up and down on the mast, via the Kelly rod mechanism to the boring tool, in order to produce the contact pressure necessary for removing soil. For this purpose locking pockets are fitted to all the Kelly rods at specific spacings.
EP 335 059 A discloses a Kelly rod mechanism with toothed driving fillets, which permit an axial force transfer or transmission in a plurality of positions corresponding to the spacing of the tooth system.
The material used for the Kelly rod mechanism is steel in suitable alloys in order to ensure the necessary strength in operation. The torque to be transmitted decides the diameter and thickness of the Kelly rods.
Particularly in the case of greater boring depths for which correspondingly long Kelly rod mechanisms are necessary, there can be a relatively high Kelly rod mechanism weight. This is not only decisive for the design of the necessary winches and drives, but also for the statics of the mast on which the boring rod mechanism is suspended. Since, as a result of design, the boring axis must be upstream of the crawlers of the boring implement, a heavy Kelly rod mechanism means a correspondingly high tilting moment of the implement. It must be correspondingly highly ballasted for adequate stability, which in turn requires a larger and more stable crawler vehicle. This leads to higher costs and restrictions during the transportation and positioning of the boring implement.